Volume controller or potentiometer for radio receivers



Juiy 23, 1935. A. w. BAKER El AL 2,009,286

VOLUME CONTROLLER OR POTENTIOMETER FOR RADIO RECEIVERS Filed Aug. 16, 1955 fnvenzkr Arlkar' lVi/k'afiz Baker SW 6 y)?! Mzfc/wM 9 WW xbeghg Patented July 23, 1935 PATENT OFFICE VOLUME CONTROLLER OR POTENTIOM- ETER FOR RADIO RECEIVERS Arthur William Baker and Stanley Cyril Mitchell, Rockdale, near Sydney, Australia Application August 16, 1933, Serial No. 685,484 In Australia August 22, 1932 2 Claims.

This invention relates particularly to volume controllers or po'fientiometers for radio receivers though it is generally advantageously applicable to other electrical instruments or apparatus 5 wherein control or regulation of electric current is effected by means of a shunt and wherein a flat coil of wire, generally superfine wire wound on a ribbon former (or other electrical conductor), is housed in a cylindrical barrel having an arm radially revolvable in the barrel to form a rubbing electric contact against the inner flat surface of the wire coil or conductor, the coil or conductor and the arm having end leads and shunt leads, respectively, arranged in the electric circuit, as well understood.

Apparatus of the type defined is effective in operation, but fine regulation thereof is difficult owing to the necessary broad surface of the arm contactand the difiiculty of minute manipulation thereof; and also, owing to the fineness of the wire, the rubbing of the contact arm thereagainst quickly Wears through said wire and it has to be replaced.

Now this invention has been specially devised to provide a volume controller (or like electrical apparatus for other uses) of the type defined, wherein the shunt contact with the coil is effected by a roller held resiliently against the coil and adapted to be rolled around it, as distinguished from the rubbing contact of the arm used heretofore, thereby eliminating wear of the fine wire of the coil; and wherein a regulation of Vernier-like precision of the shunt contact is effected and wherein the contact surfaces of the roller are kept clean and effective by the operation of said roller.

This improved volume controller or potentiometer in a present preferred construction has the barrel of dielectric material and coil and end leads and turning spindle in the barrel end, as usual, though the coil preferably has a sheet of foil under the lead end thereof to give a relatively wide surface for the initial contact. The turning spindle has a shank extending from the barrel end thereof having a key therein or a fiat on the end thereof. The shank has an end cap and inwardly thereof is a helical spring abutting a disc. This disc abuts a bevelled collar or washer which in turn rests against a shoulder of a screwed sleeve mounted on the spindle inwardly of said collar for a spindle holding nut. A contact disc or wheel having a narrow rim with rounded edges is retained in the barrel by the spindle disc, the spring on said spindle holding it in position, that is, with the rim against the disc and against the bevelled collar and contacting the coil adjacent (Cl. till-) the barrel end. A shunt wire is affixed to a terminal in contact with the spindle, and contact is made through the spindle, the disc and the wheel to the coil. A barrel cover plate is affixed in position, as well understood.

On turning the spindle, the disc is revolved, and revolving the wheel by friction contact rolls it around the inner wall of the coil in contact therewith so that electrical connection is made between the coil and the wheel and the shunt terminal. 10

But in order that this invention may be readily carried into practical effect it will now be described with reference to the drawing accompanying and forming part of this complete specifica tion. Fig. 1 is a front elevation and Fig. 2 a side 15 elevation on line 2--2 (Fig. 1) of this improved volume controller, Fig. 3 is a schematic isometric View of the casing containing the coil, the shunt terminal contact and the roller contact stop, Fig. 4 is an enlarged section through the spindle and the parts thereon, while Fig. 5 is a section on line 5-5 Fig. 4.

The barrel 6 is shown as having a base 1 but this base may be of any such shape as the particular needs require. The barrel is preferably formed with integral end 8 having bearing 9 therein and also preferably has end cover it adapted to be sprung into the barrel recess [2. The coil i3 is wound on a ribbon former as is usual and is of such gauge and capacity as the particular needs require and is affixed in the barrel 5 by terminal bolts [4 and said bolts also have thereon terminals [5 of any approved design. The lead end of the coil l3 has a sheet of electrical conducting foil or metal l6 under it to give an assured initial contact surface. Between the ends of the coil I3 is shunt bar I! retained in place by bolt I8 having terminal l9 thereon and said bar I! has an arm 20 homing in a groove 2i in the bearing 9 adapted to contact (through intervening conducting integers), spindle 22, preferably through a metallic neck bush 23. A stop 24, integral with the shunt bar I! is provided to limit the travel of the contact wheel 35 (to be hereafter described). The coil terminals 15 and the shunt terminal 19 are isolated by lugs 25 of dielectric material, preferably integral with the barrel 6.

The spindle 22 has a reduced end 26 having a revolvable sleeve 28 with a screw thread 28A thereon and a collar 21 adapted to contact the arm 20 and/or the bush 23 and outwardly thereof is a bevelled washer 29. The end 26 of the spindle 22 protruding through the washer 29 has flats 30 thereon and the disc 3| is slidably but not rotatably held on the spindle 22 by helical spring 32 retained in place by cap 33. The disc 3! has stops 34A and 34B thereon adapted to abut the stop 24 as hereafter described.

The contact wheel 35, shaped as indicated in Fig. 2, is retained in contact between the coil l3 and the disc 3i as shown in Fig. 2 by tension of the spring 32 when the spindle 22 is in its posi tion in the barrel 6 and retained by nut 36. Any convenient turn knob, as for example 31, is provide-ol.

In operation, electric leads being connected to the respective terminals as well understood, the spindle 22 is revolved and revolveswith it the disc 35. When the wheel 35 is at the commencement of its travel, as indicated by 38, the stop 3 3A abuts the stop 24 (owing to the wheel 35 canting the disc 3! as indicated in Fig. 2) and prevents reverse rotation thereof. As the disc 35 is revolved it rolls the wheel 35 by friction contact therewith, but owing to the size and arrangement of the respective parts about two and three quarter revolutions of the disc 3! are necessary to travel the wheel 35 completely around inner periphery of the coil l3. The sizes of the several parts may of course be varied to give different ratios, but that indicated has been found to give a satisfactorily minute regulation for ordinary radio potentiometer uses. Fig. 2 illustrates how the stops 34A and 34B pass the stop 24 once the wheel 35 leaves the position indicated at 33 and said stops do not abut again until the wheel 35 reaches the position indicated at 39. With the parts as illustrated, the wheel 35 reaches its terminal positions 38 or 39 slightly ahead of the stop 34A or 343 and it is necessary to continue the rotation of the disc 3| against the stationary wheel to enable either of said stops 34A or 343 to abut the stop 24. This movement enables the operator to feel the position of the wheel 35 at either end of its travel. The friction contact between the disc 3| and the wheel 35 provides that the contact edges of each are always kept bright assuring a good electric contact. This slipping movement is particularly useful where a carbon plate is used in substitution for the wire coil l3.

Although the invention has been described as applied to volume controllers or potentiometers for radio receivers, it will be seen by those skilled in the art that the mechanism described may be readily applied to other electrical purposes or apparatus. For example it might be applied to a rheostat practically in the form herein described, while with but slight variation of the coil the apparatus may be constructed as a selector switch.

We claim:

1. Improved potentiometer comprising a cylindrical barrel closed at one end, a strip-like resistance element housed within and adjacent the wall of the barrel, contacts on the barrel to which the ends of the element are secured, a spindle centrally mounted in the closed end of the barrel, a further contact on the barrel electrically connected to the spindle, a washer mounted on the said spindle, a disc slidable on and rotatable with the spindle, a spring surrounding said spindle and a cap secured to the end of the said spindle, means in frictional driving engagement with said disc comprising a roller engaging with the resistance element, the closed end of the barrel and the said washer, and retained in position with its axis inclined to the axis of the spindle by the said disc under the action of the said. spring.

2. Improved potentiometer comprising a cylindrical barrel closed'at one end, a strip-like resistance element housed within and adjacent the wall of the barrel, contacts on the barrel to which the ends of the element are secured, a spindle centrally mounted in the closed end of the barrel, a further contact on the barrel electrically connected to the spindle, a washer mounted on the said spindle, a disc slidable on and rotatable with the spindle, the plane of the disc being at an angle to the normal to the spindle, a pair of stops on the said disc, a spring surrounding the spindle and a cap secured to the end of the spindle, means in frictional driving engagement with said disc comprising a roller engaging with the resistance element, the closed end of the barrel and the said washer and retained in position with its axis inclined to the axis of the spindle by the canted disc under the action of the said spring, a stop secured to the saidbarrel for alternative engagement with the stops on the said disc. 7

ARTHUR WILLIAM BAKER. STANLEY CYRIL MITCHELL. 

